If you have a medium MRP, a C1 slot is a good place to put a second MRP. The amount of integrity it provides is irrelevant, it's all about boosting the internal module protection your larger MRP provides up to 84% and your external module protection up to 51%.well, i'd rather have medium sized mrp instead of smallest ones.
I mean a size 1 mrp offers puny protection. 70 modules armor.
While a size 1 hrp g5 heavy/duty with deep plating gives 200 hull and 14% resists.
So usually on my combat ships, size one slots are reserved for hrp